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EPSRC Reference: EP/C522877/1
Title: Application of SQUID NMR to the study of novel p-wave 3He superfluids in regular confined geometries
Principal Investigator: Saunders, Professor J
Other Investigators:
Cowan, Professor B Lusher, Dr C
Researcher Co-Investigators:
Dr AJ Casey
Project Partners:
Cornell University Hitachi Europe Ltd Unlisted Inst
Department: Physics
Organisation: Royal Holloway, Univ of London
Scheme: Standard Research (Pre-FEC)
Starts: 01 April 2005 Ends: 30 September 2008 Value (£): 518,606
EPSRC Research Topic Classifications:
Materials Characterisation
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
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Summary on Grant Application Form
Superconductivity is a remarkable state of matter found in electrical conductors at sufficiently low temperatures, arising because the electrons form pairs. It is sometimes helpful to think of these pairs as rather like diatomic molecules. All pairs are in the same quantum state. Because of this the large scale properties of superconductors are governed by the laws of quantum mechanics, and this leads to important applications. For example a device based on a ring of superconductor, in which the superconductivity is deliberately weakened at two points can be used as an extremely sensitive detector of magnetic fields. This is the Superconducting QUantum Interference Device or SQUID.Liquid 3He becomes superfluid at temperatures of a few mK. The 3He atoms behave rather like uncharged electrons, and the superfluidity also occurs because the 3He atoms form pairs. But because the 3He atom is rather like a tiny billiard ball, and because of the nature of the pairing interaction, the pairs orbit around one another (with one unit of orbital angular momentum), and the superfluid is anisotropic. Since the discovery of superfluidity in 3He, a steadily increasing list of materials have been synthesised which, under the right conditions, exhibit a similar or related form of so called unconventional superconductivity. 3He is important to achieving a fundamental understanding of unconventional superfluidity because at low temperatures we just have the pairs to look at, there is no lattice (the normal state is isotropic), and it is extremely pure.The nucleus of each 3He atom is a tiny magnet and each 3He pair has three possible magnetic quantum states. These combine with the possible orbital states to give the pair wavefunction (order parameter) and there are many possibilities in principle. But the equilibrium state is that of lowest energy; three different states are selected, depending on external conditions such as temperature, pressure and magnetic field. These states can be fingerprinted by Nuclear Magnetic Resonance (NMR) Spectroscopy.We will investigate what happens when you squeeze liquid 3He into a small regular space, like a thin slab or a narrow cylinder, of size comparable to the pair diameter, which can be varied from 72nm to 14nm by applying external pressure. With modem nanofabrication techniques, as well as by growing thick films, it is possible to form such a sample. And in our laboratory we have developed sensitive NMR spectrometers based on SQUID detectors. Their unprecedented sensitivity allows us to probe these tiny volumes of liquid 3He to temperatures as low as 200 microKelvin for the first time.There are many theoretical predictions, including of several exotic new phenomena. In sufficiently thin slabs the superfluid is effectively two dimensional; the recent history of the study of matter contains many examples of new effects that have emerged when we enter worlds of reduced dimensionality. We expect that the knowledge we gain from trying to understand something as deceptively simple as 3He will impact on research on the new superconducting materials and their eventual application in devices using thin film technology. Moreover this fundamental science provides one powerful impetus to improve the sensitivity of our SQUID NMR spectrometers still further, with implications for the wider application of the NMR method.
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